Conventional combustion processes have associated CO2 emissions that have been identified as an area for potential reduction of greenhouse gas emissions within refineries.
Technologies such as amine scrubbing can remove CO2 from process gas streams, such as the flue gas waste stream from combustion processes such as a steam methane reformer (SMR) furnace or a fluidized catalytic cracker (FCC) regenerator. Combustion processes typically involve combustion of a fuel (for example natural as for an SMR furnace or coke for an FCC regenerator) using air as the oxidant. Because the fuel is burned in the presence of air, the exiting flue gas comprises mostly nitrogen. While the concentration of CO2 in the flue gas is relatively low, the flow rate is large, such that a majority of a refinery's total CO2 emissions are emitted during combustion processes. Some of the remaining CO2 comes from reaction processes where it is produced in a stream with a relatively high CO2 partial pressure (typically around 45 psia), such that the CO2 can be effectively captured using amine scrubbing technology. On the other hand, combustion flue gas streams are mostly nitrogen, thus it is cost prohibitive to size an amine scrubber to process the entire streams. The result is an upper limit to how much CO2 could be captured practically in a refinery. This could have a significant impact on the economics of individual combustion processes or an entire refinery if CO2 emission taxes, incentives, and/or caps were imposed.
One way that others have proposed to solve this problem is by using an oxygen-fuel combustion process instead of conventional combustion processes. In oxygen-fuel combustion process, the fuel is combusted in an oxygenated environment rather than air. The resulting flue gas primarily consists of CO2 and H2O with very little nitrogen. The H2O in the fine gas is easily removed through condensation, leaving, a stream of concentrated CO2 that is ready for compression, transportation and sequestration. This process greatly increases the amount of CO2 that could be captured practically from a combustion process.
One of the largest obstacles in operating an oxygen-fuel combustion process is obtaining oxygen. Typically, the only proposed method of obtaining oxygen to a combustion process is the use of an air separation unit. The problems with air separation units is that they typically separate oxygen and nitrogen from air through a cryogenic separation process, which has large capital, operating costs and CO2 footprint associated. An example of technology that is able to provide large quantities of oxygen to SMR boiler furnace is U.S. Provisional 61/673,021, hereby incorporated by reference.
There exists a need to produce and deliver oxygen in high quantities and purity in a safe and cost effective manner to operate with oxygen-fuel combustion processes.